Bearing preload structure of machine tool

Abstract

On an outer surface 2 b of a spindle 2 , a first end surface 2 f abutting on one end surface 11 d in an axial direction of an inner ring 11 of a first ball bearing 10 is formed so as to be positioned in a plane perpendicular to an axial center, and a second end surface 2 c is formed so as to be parallel to the first end surface 2 f and be positioned a predetermined distance t apart in the axial direction from the other end surface 11 c ′ in the axial direction of an inner ring 11 ′ of a second ball bearing 10 ′, and a flange member 17 is attachably/detachably fitted to the second end surface 2 c so as to come into close contact with the second end surface 2 c , and between the flange member 17 and the other end surface 11 c ′ of the inner ring 11 ′, a collar member 19 having an axial-direction dimension slightly longer than the predetermined distance t is interposed.

What is claimed is: 
     
       1. A bearing preload structure of a machine tool, in which a ball bearing arrangement made by interposing a plurality of balls between an inner ring and an outer ring, is interposed between an outer peripheral surface of a spindle and an inner peripheral surface of a spindle head and thereby the spindle is rotatably supported by the spindle head, which receives a preload force in an axial direction to act on the ball bearing arrangement, the bearing preload structure comprising:
 a first end surface that is formed on a bearing fitting part of the outer peripheral surface of the spindle and projects toward a side opposite to an axial center from the outer peripheral surface and abuts on a first axial end surface of the inner ring; 
 a second end surface formed on the bearing fitting part of the outer peripheral surface of the spindle so as to be parallel to said first end surface and step down to an axial center side from the outer peripheral surface; 
 a flange member having a pressing surface, the flange member being secured to the second end surface by bolts; and 
 the ball bearing arrangement comprising a first ball bearing has one inner ring and one outer ring and a second ball bearing has one inner ring and one outer ring and disposed therebetween is: an inner ring spacer that restricts axial-direction positions of the inner rings of the first ball bearing and the second ball bearing, and an outer ring spacer that restricts axial-direction positions of the outer rings of the first ball bearing and the second ball bearing, wherein 
 said first end surface is formed so as to abut on an end surface of the inner ring of said first ball bearing, on a side opposite to said second ball bearing, 
 said second end surface is formed so as to be positioned a predetermined distance t apart in the axial direction from an end surface of the inner ring of said second ball bearing, on a side opposite to said first ball bearing, 
 a collar member is interposed between the end surface of the inner ring of said second ball bearing, on the side opposite to said first ball bearing and the pressing surface of said flange member, 
 the collar member is a separate structural member that is distinct from the flange member, 
 the collar member is configured by securing the flange member to the second end surface by the bolts, 
 the collar member has a cylindrical structure of which an inner diameter is constant through an entire length thereof, and is slidable with respect to the spindle, and 
 the collar member, when not installed in the bearing preload structure, has an axial direction length longer than the predetermined distance t.